1. Field of the Invention
The present invention relates to a reproduced signal waveform control device for a MR (magneto-resistive) head, and particularly to a reproduced signal waveform control device for realizing a magnetic recording device capable of high recording density and high reliability.
2. Description of the Related Art
Ever greater recording density is being sought for magnetic recording devices connected to small host computers, and tests are being conducted to introduce new technology including heads in which MR (magneto-resistive) elements are used in the reproducing element (hereinbelow referred to as "MR heads") and PRML (Partial Response Maximum Likelihood) signal processing technology. The waveform of a reproduced signal of magnetic recording devices employing these MR heads, however, exhibits a great variance between the output amplitude/half power width of positive pulses and the output amplitude/half power width of negative pulses (hereinbelow referred to as "asymmetry"), and this problem has been a problem for achieving higher density in magnetic recording devices. The effect of this asymmetry is particularly pronounced when an MR head and PRML signal processing technology are used simultaneously and has posed a barrier to achieving higher density.
Various methods have been proposed for reducing this asymmetry. The invention of Japanese Patent Laid-open No. 205903/92, for example, proposes a method in which the peak value of the positive pulse and the peak value of the negative pulse in one isolated pulse are detected, and the difference between the two is taken and optimized. However, because only one isolated pulse or individual isolated pulses are detected, this invention suffers from the drawback of not being able to adequately cope with the characteristic of various components operating under different conditions within a device, or with cases in which conditions or state changes or the characteristic of an isolated wave differs from the average characteristic. Moreover, with the trend in recent years toward narrower tracks, there is a growing demand for smaller MR elements, and this has given rise to the problem of fluctuation in asymmetry during operation of a device (hereinbelow referred to as "instability"). The above-described prior art has been completely unable to cope with such instability in asymmetry during operation, and as a consequence, there has been a call for the development of new signal processing methods and circuits.